php生成验证码并检验

<?php
session_start();

// 生成随机字符串
function generateRandomString($length = 6) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }
    return $randomString;
}

// 生成验证码并保存到session
$verifyCode = generateRandomString();
$_SESSION['verifyCode'] = $verifyCode;

// 创建图像
$image = imagecreatetruecolor(100, 30);
$backgroundColor = imagecolorallocate($image, 255, 255, 255);
$textColor = imagecolorallocate($image, 0, 0, 0);

imagefilledrectangle($image, 0, 0, 100, 30, $backgroundColor);
imagettftext($image, 20, 0, 15, 25, $textColor, 'arial.ttf', $verifyCode);

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>

<?php
session_start();

if (isset($_POST['verifyCode']) && $_POST['verifyCode'] === $_SESSION['verifyCode']) {
    echo "验证码正确";
} else {
    echo "验证码错误";
}
?>